This invention relates to a rubber composition and a fuel transporting hose for a vehicle. More particularly, this invention relates to a fuel transporting hose for a vehicle which is simple and inexpensive in construction and is satisfactory for fuel impermeability and a certain level of conductivity as required of a fuel transporting hose for a vehicle, and to a rubber composition used therefor.
Regulations concerning the permeation of fuel in a vehicle, which are similar to the so-called SHED regulation in the United States, are put into effect in A.D. 2000 in Japan and Europe. As is well known, a fuel transporting hose is highly responsible for the permeation of fuel in a vehicle, and measures have been sought for controlling the permeation of fuel from a fuel transporting hose.
It has been a common practice in Japan to use FKM (fluororubber) of high fuel impermeability and sour resistance to form an inner wall layer of a fuel hose used in what is called a liquid line, such as a feed or return circuit in a vehicle fuel line. Generally used NBR (acrylonitrile-butadiene rubber), or NBR-PVC which is a blend of NBR and PVC (polyvinyl chloride), has been used for a filler neck hose connecting a filler hole and a gasoline tank, or a breather or evaporation hose forming a vapor line. In the United States having the SHED regulation already in effect, the specifications for a filler neck hose or an evaporation hose employ FKM or a resinous material such as a polyamide resin or fluororesin for its inner wall layer and NBR-PVC, ECO (epichlorohydrin rubber), CSM (chlorosulfonated polyethylene rubber) or the like for its outer wall layer.
The specifications adopted in Japan for the filler neck, breather and evaporation hoses as mentioned above, however, fail to attain any fuel impermeability conforming to the national regulation going to be put into effect as stated above. The filler neck or evaporation hose having an inner wall layer formed from FKM or a resinous material as in the United States can be expected to satisfy the regulation in fuel impermeability. FKM or a fluororesin is, however, expensive, and is so low in reactivity that its bonding to an outer layer material requires an additional level of technical skill and an additional amount of processing cost. Another drawback is that a complicated manufacturing process is required for shaping a hose having a layer of FKM like bellows.
It has also been pointed out that a filler neck or breather hose may be charged with static electricity as a result of e.g. the flow of gasoline during fill-up or body vibration and may produce a spark when contacted by a metallic fill-up gun, resulting in the ignition of gasoline. It is, thus, hoped that conductivity will be imparted to any such hose (for example, to the extent giving it a volume specific resistance not exceeding 108xcexa9xc2x7cm) to prevent any electrical charging thereof. It is, however, difficult to impart any satisfactory conductivity, since FKM or a resinous material essentially has a high electric resistance.
Under these circumstances, it is an object of this invention to make a fuel transporting hose for a vehicle having high fuel impermeability and conductivity by using a simple and inexpensive rubber composition. The inventor of this invention has evaluated various rubber compositions containing NBR or NBR-PVC as a base material, and has conceived a compound design for a rubber composition which is comparable to FKM in fuel impermeability and exhibits high conductivity, while ensuring the necessary properties including low temperature properties.
It has been pointed out that NBR or NBR-PVC having a relatively high AN content of, say, 36 to 42 percent by weight has an improved fuel swelling resistance. However, the inventor""s experiment conducted by using PHASE 11 gasoline for evaluation (gasoline for a permeation test as specified by the U.S. CARB, i.e. SHED test) indicates that NBR or NBR-PVC having such an content is apparently unsatisfactory in fuel impermeability.
During the process of research work, on the other hand, the inventor has found that NBR or NBR-PVC having a specific AN content in an ultrahigh nitrite range (for example, 43 percent by weight or higher) has a high fuel impermeability comparable to that of FKM. The inventor has also found that, while it is feared that NBR or NBR-PVC having an content in an ultrahigh nitrite range may be undesirably poor in low temperature properties as required of a fuel hose for a vehicle (the flexibility of a hose used in a very cold place having a temperature of as low as, say, xe2x88x9230xc2x0 C.), the addition of a properly selected plasticizer in a properly selected amount makes it possible to realize a satisfactory level of low temperature properties while ensuring a high fuel impermeability, and that the proper addition of carbon black (CB) makes it possible to realize satisfactory conductivity while ensuring the properties mentioned above.
Moreover, the inventor has found very interesting matters, as shown at (1) to (4) below, about the technical meaning of PVC as a material blended for such a rubber composition.
(1) PVC is basically a component contributing to fuel impermeability, and it is necessary or beneficial to blend PVC with NBR to impart weatherability and ozone resistance to a rubber composition used for making an outer layer for a fuel hose having a multilayer wall structure, or a fuel hose having a single-layer wall. A rubber composition containing 25 percent by weight or more of PVC relative to NBR is practically satisfactory in weatherability and ozone resistance.
(2) It is, therefore, not necessary to blend 25 percent by weight or more of PVC with NBR to make any rubber composition not used for the purpose as stated at (1) above. On the other hand, it is feared that PVC as a resinous component may lower the low temperature properties of the composition. While it is effective in this connection to increase the proportion of the plasticizer, the excessive increase of the plasticizer in the rubber composition results in a reduction of its fuel impermeability. Thus, an increase in the blend ratio of PVC brings about a narrowing in the range of proportions which can be selected for achieving a good balance between the fuel impermeability of the rubber composition and its low temperature properties.
(3) If the amount of PVC blended is less than 25 percent by weight relative to NBR, it is possible to secure a broad range of proportions which can be selected for making a rubber composition having a good balance between fuel impermeability and low temperature properties, while maintaining the contribution of PVC to fuel impermeability as stated above. The amount of PVC is preferably not more than 5 percent by weight if the balance between the fuel impermeability of the rubber composition and its low temperature properties is more important than the contribution of PVC to its fuel impermeability.
(4) If NBR has an content set in a really ultrahigh range not lower than 46 percent by weight, the contribution of PVC to fuel impermeability as stated above can hardly be obtained. In such a case, therefore, it is preferable in view of the foregoing (1) to (3) to use NBR as a base material without blending any PVC.
According to a first aspect of this invention, there is, thus, provided a rubber composition for a fuel transporting hose for a vehicle which comprises NBR having an AN (combined acrylonitrile) content of 46 to 52 percent by weight as a base material, and 15 to 30 parts by weight of a plasticizer having an SP value (solubility parameter) of 8.8 or more and a molecular weight of 550 or less, relative to 100 parts by weight of the base material.
According to the first aspect of this invention in which NBR having an AN content of 46 to 52 percent by weight is used as a base material, NBR having such an ultrahigh AN content makes it possible to obtain a high fuel impermeability comparable to that of FKM. The composition contains 15 to 30 parts by weight of a plasticizer having the SP value and molecular weight stated above relative to 100 parts by weight of the base material. The plasticizer having a molecular weight of 550 or less is low in viscosity at a low temperature and markedly improves the low temperature properties of the rubber composition. The plasticizer having an SP value of 8.8 or more is well miscible with NBR or NBR-PVC having the AN content stated above and does not substantially affect the fuel impermeability of the rubber composition. Therefore, the rubber composition exhibits both a high level of fuel impermeability and a satisfactory level of low temperature properties. Moreover, the proper addition of carbon black (CB) makes it possible to realize a satisfactory level of conductivity, while ensuring the various properties as stated above. If the plasticizer has an SP value of less than 8.8, its deficiency in solubility with the base material causes its bleeding and it may fail to contribute effectively to improving the low temperature properties of the rubber composition. If the plasticizer has a molecular weight exceeding 550, its deficiency in viscosity at a low temperature may fail to contribute effectively to improving the low temperature properties of the rubber composition. If the plasticizer has a proportion of less than 15 parts by weight, its addition may not prove to be satisfactory, and if its proportion exceeds 30 parts by weight, it is feared that it may adversely affect the fuel impermeability of the rubber composition and may bleed from the base material. The rubber composition according to the first aspect of this invention is unsuitable as a material for an outer wall layer of a fuel hose having a multilayer wall structure, or for a fuel hose having a single-layer wall, since it does not have any PVC blended with NBR.
According to a second aspect of this invention, there is provided a rubber composition for a fuel transporting hose for a vehicle which comprises a blended base material obtained by blending NBR having an AN content of 46 to 52 percent by weight and PVC in an amount of less than 25 percent by weight relative to NBR, and 15 to 30 parts by weight of a plasticizer having an SP value of 8.8 or more and a molecular weight of 550 or less, relative to 100 parts by weight of the base material.
According to the second aspect of this invention which employs a blended base material obtained by blending NBR having an AN content of 46 to 52 percent by weight and less than 25 percent by weight of PVC, the action of NBR having an ultrahigh AN content and a certain contribution of PVC to fuel impermeability make it possible to achieve a high level of fuel impermeability which is comparable to that of FKM. The composition also contains the same amount of the same plasticizer as in the first aspect of this invention. Therefore, it is possible to obtain various operations and efffects from the addition of a proper amount of a plasticizer having a proper SP value and molecular weight, as is the case with the first aspect of this invention. The effects by the proper addition of carbon black (CB) can also be obtained. The rubber composition according to the second aspect of this invention is unsuitable as a material for an outer wall layer of a fuel hose having a multilayer wall structure, or for a fuel hose having a single-layer wall, since it has a PVC proportion of only less than 25 percent by weight relative to NBR. As its proportion is less than 25 percent by weight, PVC does not appreciably affect a good balance between the fuel impermeability of the rubber composition and its low temperature properties.
According to a third aspect of this invention, the rubber composition according to the first or second aspect thereof satisfies one or more of the following (1) to (4):
(1) NBR has an AN content of 48 to 52 percent by weight;
(2) the plasticizer has an SP value of 9.0 or more;
(3) the plasticizer has a molecular weight of 450 or less; and
(4) the plasticizer has a proportion of 20 to 25 parts by weight relative to 100 parts by weight of the base material.
The rubber composition satisfying one or more of the foregoing (1) to (4) is a particularly good rubber composition.
According to a fourth aspect of this invention, the rubber composition according to any of the first to third aspects thereof satisfies the following (5) and/or (6):
(5) it has a volume specific resistance not exceeding 108xcexa9xc2x7cm; and
(6) it has a hardness of 55 to 75 degrees as measured by a JIS K6253 (ISO 48) durometer, type A.
The good conductivity of the rubber composition containing a proper amount of a proper type of CB and thereby satisfying the foregoing (5) makes it possible to prevent effectively any inconvenience caused by an electrostatic charge, including sparking during fill-up, as mentioned before. The rubber composition having a hardness satisfying the foregoing (6) as measured by a JIS K6253 (ISO 48) durometer, type A, owing to the proper addition of plasticizer and CB can make a fuel hose for a vehicle having a practically suitable level of hardness or softness.
According to a fifth aspect of this invention, there is provided a fuel transporting hose for a vehicle having an inner wall layer formed from a rubber composition according to any of the first to fourth aspects of this invention and an outer wall layer formed from a rubber material of high weatherability and ozone resistance, and further including a reinforcing yarn layer formed between the inner and outer wall layers, if required.
The rubber composition according to any of the first to fourth aspects of this invention is low in weatherability and ozone resistance, since its base material is NBR not blended with PVC, or NBR blended with only less than 25 percent by weight of PVC, though it has a good balance between fuel impermeability and low temperature properties and good conductivity. The construction of the fuel transporting hose for a vehicle according to the fifth aspect of this invention ensures its high weatherability and ozone resistance, while it retains the advantages of the rubber composition, such as its fuel impermeability and good conductivity. The reinforcing yarn layer between the inner and outer wall layers ensures an improved hose strength as an additional advantage.
According to a sixth aspect of this invention, there is provided a fuel transporting hose for a vehicle having an inner wall layer formed from a rubber composition as set forth at (7) below and an outer wall layer formed from a rubber composition as set forth at (8) below, and further including a reinforcing yarn layer formed between the inner and outer wall layers, if required:
(7) a rubber composition comprising: as a base material NBR having an AN content of 48 to 52 percent by weight, or such NBR blended with less than 5 percent by weight of PVC; and 15 to 25 parts by weight of a plasticizer having an SP value of 8.8 or more and a molecular weight of 550 or less, relative to 100 parts by weight of the base material; and
(8) a rubber composition comprising: as a base material a blend of NBR having an AN content of 43 to 50 percent by weight and 25 to 40 percent by weight of PVC; and 15 to 35 parts by weight of a plasticizer having an SP value of 8.8 or more and a molecular weight of 550 or less, relative to 100 parts by weight of the base material.
The rubber composition (7) for the inner wall layer of the hose according to the sixth aspect of this invention contains as its base material NBR having an AN content shifted to the ultrahigh side as compared with the rubber composition according to the first aspect of this invention, or NBR-PVC containing a very small amount of PVC as compared with the rubber composition according to the second aspect of this invention, and further contains a similar amount of a similar plasticizer. Therefore, the rubber composition has a particularly good balance between its fuel impermeability and low temperature properties, and as there is no substantial meaning in blending PVC with NBR having an ultrahigh AN content of 48 to 52 percent by weight, the rubber composition hardly has its fuel impermeability affected, even if the amount of PVC is less than 5 percent by weight, or even zero. The rubber composition (8) for the outer wall layer is of satisfactorily high weatherability and ozone resistance, while having certain levels of fuel impermeability and low temperature properties at the same time, as stated at (1) before. Thus, the hose according to the sixth aspect of this invention is comparable or even superior in fuel impermeability to that according to the fifth aspect thereof, can realize good conductivity, and can also realize low temperature properties as required. The reinforcing yarn layer further formed between the inner and outer wall layers brings about an improved hose strength as an additional advantage to the fuel transporting hose according to the sixth aspect of the invention.
According to a seventh aspect of the invention, there is provided a fuel transporting hose for a vehicle in which the rubber composition (7) according to the sixth aspect of this invention satisfies one or more of the following (9) to (12) and/or the rubber composition (8) according to the sixth aspect of this invention satisfies one or both of the following (10) and (11):
(9) NBR has an AN content of 50 to 52 percent by weight;
(10) the plasticizer has an SP value of 9.0 or more;
(11) the plasticizer has a molecular weight of 450 or less; and
(12) the plasticizer is added in an amount of 18 to 23 parts by weight relative to 100 parts by weight of the base material.
According to the seventh aspect of this invention, it is possible to realize a particularly good rubber composition if the rubber composition (7) according to the sixth aspect of this invention satisfies one or more of (9) to (12).
According to an eighth aspect of this invention, there is provided a fuel transporting hose for a vehicle in which the rubber composition (7) and/or (8) according to the sixth or seventh aspect of this invention satisfies the following (13) and/or (14):
(13) the rubber composition has a volume specific resistance not exceeding 108xcexa9xc2x7cm; and
(14) it has a hardness of 55 to 75 degrees as measured by a JIS K6253 (ISO 48) durometer, type A.
According to the eighth aspect of this invention, the good conductivity of the rubber composition (7) and/or (8) containing a proper amount of a proper type of CB and thereby having its volume specific resistance adjusted as stated at (13) makes it possible to prevent effectively any inconvenience caused by an electrostatic charge, including sparking during fill-up, as mentioned before. The rubber composition having its hardness adjusted as stated at (14) owing to the proper addition of plasticizer and CB can make a fuel hose for a vehicle having a practically suitable level of hardness or softness.
According to a ninth aspect of this invention, there is provided a fuel transporting hose for a vehicle having an inner wall layer formed from the rubber composition (7) according to any of the sixth to eighth aspects of this invention and an outer wall layer formed from a rubber material of high weatherability, ozone resistance and cure flatting (flatting during curing) resistance, and further including a reinforcing yarn layer formed between the inner and outer wall layers, if required.
The rubber composition (7) according to any of the sixth to eighth aspects of this invention tends to lack flatting resistance during cure under heat, since its base material is NBR having an ultrahigh AN content, or NBR blended with only less than 25 percent by weight of PVC, though it has a good balance between fuel impermeability and low temperature properties and good conductivity. The construction of the hose according to the ninth aspect of this invention ensures its high weatherability, ozone resistance and cure flatting resistance, while it retains the advantages of the rubber composition, such as its fuel impermeability, low temperature properties and conductivity. As one of its specific advantages, its pan cure with no mandrel can be carried out without any problem, even if the hose may be of a relatively large diameter like a breather hose. The reinforcing yarn layer further formed between the inner and outer wall layers ensures an improved hose strength as an additional advantage to the fuel transporting hose according to the ninth aspect of the invention.